embed xexpr-path

1 files changed, 99 insertions, 0 deletions

diff --git a/ebus-racket/ebus/xexpr-path/main.rkt b/ebus-racket/ebus/xexpr-path/main.rkt
new file mode 100644
index 0000000..97e7f81
--- /dev/null
+++ b/ebus-racket/ebus/xexpr-path/main.rkt
@@ -0,0 +1,99 @@
+#lang racket/base
+;
+; XML-Expression Path Lookup
+;
+
+(require racket/contract
+         racket/string
+         racket/match
+         racket/dict
+         racket/list
+         xml)
+
+(provide xexpr-path-first
+         xexpr-path-list
+         xexpr-path-text
+         xexpr-path/c)
+
+
+(define xexpr-path/c
+  (listof (or/c symbol?
+                (list/c symbol? string?)
+                (list/c symbol?))))
+
+
+(define (children element)
+  (match element
+    ((list tag (list (list name value) ...) children ...)
+     children)
+
+    ((list tag children ...)
+     children)
+
+    (else
+     null)))
+
+
+(define (attr-value?? name value)
+  (lambda (v)
+    (equal? (dict-ref (attributes v) name #f) value)))
+
+
+(define (tag-name?? name)
+  (lambda (v)
+    (or (eq? name '*)
+        (and (pair? v)
+             (eq? (car v) name)))))
+
+
+(define (attributes element)
+  (match element
+    ((list tag (list (list name value) ...) children ...)
+     (for/list ((n (in-list name))
+                (v (in-list value)))
+       (cons n v)))
+
+    (else
+     null)))
+
+
+(define (path-item-procedure item)
+  (match item
+    ((list attr-name attr-value)
+     (lambda (tags)
+       (list (filter (attr-value?? attr-name attr-value) tags))))
+
+    ((list attr-name)
+     (lambda (tags)
+       (list
+         (filter values
+                 (for/list ((tag (in-list tags)))
+                   (dict-ref (attributes tag) attr-name #f))))))
+
+    (tag-name
+     (lambda (tags)
+       (for/list ((tag (in-list tags)))
+         (filter (tag-name?? tag-name) (children tag)))))))
+
+
+(define/contract (xexpr-path-list path xexpr)
+                 (-> xexpr-path/c xexpr/c (listof (or/c xexpr/c string?)))
+  (let ((pipeline (append* (for/list ((item (in-list path)))
+                             (list (path-item-procedure item) append*)))))
+    ((apply compose (reverse pipeline)) (list xexpr))))
+
+
+(define/contract (xexpr-path-first path xexpr)
+                 (-> xexpr-path/c xexpr/c (or/c xexpr/c string? #f))
+  (let ((results (xexpr-path-list path xexpr)))
+    (and (not (null? results))
+         (first results))))
+
+
+(define/contract (xexpr-path-text path xexpr)
+                 (-> xexpr-path/c xexpr/c (or/c #f string?))
+  (let ((results (xexpr-path-list path xexpr)))
+    (string-append* (map xexpr->string results))))
+
+
+; vim:set ts=2 sw=2 et: